Accessibility inspector contrast issue

I have set the text color to label is #646464, but after running the accessibility inspector on device (iPhone 6) it gives me a contrast color warning. Please find attached screenshot.

The conflict is between text color set for UILabel #646464 and inspector saying that is #777777.

Also, it asks me to increase font size, If I do this it's still showing warning and I don't want to increase font size.

Why does accessibility inspector give me such warning?

How I can fix this warning?

Please let me know as I'm stuck for a long time.